1. Field of the Invention
The present invention relates to systems and methods for controlling the stopping position of an engine crankshaft during engine shutdown to provide a favorable position for restarting.
2. Background Art
One concept for improving fuel consumption of a vehicle is to shut down the internal combustion engine if there is no requirement for power instead of allowing it to continue to idle. One application is stop and go traffic that may occur in traffic jams on freeways as well as at traffic lights, railroad crossings, etc.
One problem with the concepts that shut down the internal combustion engine when it is not required to improve fuel consumption is the necessity to start the internal combustion engine again. When the engine is shut down in an uncontrolled way, the crankshaft and the camshaft stop in an unknown random position. Consequently, the position of the pistons in the individual cylinders of the engine is also unknown and is left to chance. Accurate crankshaft position information is, however, useful for restarting the engine in an uncomplicated manner that is as fast and efficient as possible and thus saves fuel. For example, in engines with direct injection, it is possible to start or restart the engine directly from the stationary state without a starter motor by injecting fuel directly into the combustion chambers and igniting the fuel/air mixture using a spark plug. To be carried out successfully, it is advantageous if the crankshaft is at or near a specific position at the commencement of the starting so that at least one piston is in a position where a fuel injection and subsequent ignition of the air/fuel mixture lead to movement of the piston within the cylinder. In a four-stroke internal combustion engine, the piston would have to be in the expansion or working stroke with at least one associated exhaust valve closed. As such, this method for direct starting or restarting requires an accurate indication of the crankshaft position or piston position to select appropriate cylinders for the fuel injection to start the engine.
In an internal combustion engine equipped with an electronically regulated ignition and/or an electronically regulated injection, markers arranged on the crankshaft supply signals about the crankshaft position to sensors which are connected to the engine control system to control the ignition time and the injection time. However, these sensors require rotation of the crankshaft to provide a signal and provide ambiguous information for a number of cylinder firings immediately after starting or restarting the engine so that some time is required to synchronize the crank angle position and the engine control parameters. In addition, devices have to be provided for starting or restarting the engine, such as a conventional starter motor, electric motor, or a similar device suitable for rotating the crankshaft.
Various concepts have been proposed in the prior art for controlling the stopping position of the crankshaft (or adjusting the position after the engine is stopped) and for restarting the engine. These concepts may generally be categorized as either active or passive. The active adjustment devices either require additional components, such as an additional electric motor, to apply an adjustment torque, or operate using an additional fuel injection or ignition in the same way as when selective combustion processes are initiated to set the predefined crank angle position. Concepts employing active devices that require additional fuel or electrical energy are contrary to the basic goal of shutting down the engine to save fuel or energy to improve fuel economy.
Passive adjustment devices may use the rotational movement of the crankshaft during shut down after fuel and/or ignition have ended to control the stopping position of the crankshaft in a predefined advantageous position. For example, an intake/exhaust (gas exchange) valve control system may be used as a passive adjustment device to exert a stopping or braking force on the engine or crankshaft to control the deceleration of the shaft and its stopping position. This requires a relatively complex and costly variable valve control system. Many of the disclosed concepts are not suitable for controlling the stopping position of the crankshaft with the necessary accuracy to facilitate direct restart.